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Kiritimati Reed-warbler Acrocephalus aequinoctialis
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This species is listed as Endangered because it is suspected to be confined to just two coral atolls in the Northern Line Islands, Kiribati. It has already been extirpated from one atoll and declines are suspected within the remaining occupied range.

Taxonomic source(s)
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.

Taxonomic note


15 cm; 19 g. A medium-sized, predominantly grey reed-warbler with white feather edgings. Has obscure whitish supercilium extending from bill base backwards, olivaceous-grey cheek; above, olivaceous-grey, neutral grey on neck side and scapulars, many feathers with whitish margins, these narrow on back, broader on rump and undertail-coverts. Sexes alike. Juvenile is brighter grey than adults. Race pistor is larger than nominate. Voice. Calls "cha", "che" and "churr". Song is simple in comparison to congeners and involves the call notes above repeated in phrases of varying amplitude.

Distribution and population
Acrocephalus aequinoctialis is endemic to Kiritimati (Christmas Island) and Teraina (Washington) islands in the Northern Line Islands, Kiribati. It remained common on Teraina in 1980 (Gupta 2007). It formerly occurred on Tabueran (Fanning), but was apparently extirpated in 1972. It was described as 'common' on Kiritimati in 1966 (Pratt et al. 1987), but just 400 individuals were estimated there in 1972 and it was 'scarce in the vicinity of settlement' by 1980 (Sherley 2001). Surveys on Kiritimati in 2007-2011 indicate that the species is widespread and locally common on the mainland and individuals occasionally visit small motu in the lagoons (R. Pierce in litt. 2012). Distribution on Kiritimati is patchy, e.g. there are large areas in the south-east of the island where the warbler is absent due to unsuitable habitat. Densities of up to 50 birds/km2 have been reported on Kiritimati (Pierce et al. 2007).

Population justification

Pierce et al. (2007) recorded densities of up to 50 birds/km2 on Kiritimati and pairs reportedly occupy a territory of 1.8-2.3 ha, which coarsely equates to 100 mature individuals/km2. Combined, the islands of Kiritimati and Teraini have a land area of 336 km2, suggesting they could support a maximum of c.16,000-30,000 mature individuals. However, the species is absent from considerable areas of these two islands, likely due to unsuitable habitat, and occurs at lower densities, especially where invasive predators are present. Consequently a global population of 2,500-9,999 mature individuals is suspected, though this may prove to be an overestimate and further surveys are required. This is equivalent to 3,750-14,999 individuals in total, rounded here to 3,500-15,000 individuals.

Trend justification
Population trends have not been empirically assessed, but the species has been extirpated from one island (Tabueran in the 1970s), and threats within its extant range include introduced predators and habitat degradation driven by a variety of processes. Consequently the species is suspected to be experiencing moderately rapid declines. However, on Kiritimati, monitoring has been ongoing since 2007, but no declines have been detected (R. Pierce in litt. 2012). Should the species be found not to be declining overall, it would warrant downlisting to a lower threat category.

It occurs in vegetated areas with scattered dominant Tournefortia argentea trees (growing 4-6 m) and Cassytha filiformis mixed with dense Scaevola and many other indigenous shrubs, and sometimes with introduced coconut palms (Cocos nucifera), but not in areas with dense coconuts palms. It is absent from areas that have been cleared or recently burned (R. Pierce in litt. 2012). Birds will cross relatively open grassy areas or sandflats and cross up to 300 m to access motu that have recently been cleared of Rattus exulans (R. Pierce in litt. 2012). The species has also been sighted in gardens close to human habitation (T. Mark in litt. 2010). It feeds on insects, including flies and dragonflies; and small lizards. It spends much of its time foraging on the ground, in low ground cover, and in dead or low branches close to ground level. It is sedentary and a weak flier. Breeding occurs from at least February-July. It is reportedly monogamous; females incubating 2-4 eggs in nests placed just below the canopy of Tournefortia argentea. The territory size is reportedly 1.8-2.3 ha. Maximum densities recorded in 2007 were 0.5 birds/ha (R. Pierce in litt. 2012).

The land areas of Kiritimati and Teraina are 322 km2 and 14 km2 respectively, and both support introduced rats Rattus spp.and cats Felis catus (A.Wegmann in litt. 2008), although the spread of black rats R. rattus on Kiritimati appears to have slowed or possibly stopped, with black rats being relatively rare beyond the inhabited areas of the island and outer beaches (R. Pierce in litt. 2012). Although the rate of spread of R. rattus has been unusually slow, it does need monitoring. The successful management of T. argentea trees is likely to be a significant factor for the species (T. Mark in litt. 2010). Hunting by children with slingshots may also pose a threat (A.Wegmann in litt. 2008). Kiritimati Atoll is also suffering from poorly planned immigration leading to widespread degradation of remaining habitats (J. Millet in litt. 2008); principal threats include habitat loss from fires, clearing for coconuts, development and habitat modification (e.g. proliferation of the weed Pluchea indica following fire [Pierce et al. 2007]).

Conservation Actions Underway
A survey for the species gathered information on baseline population density, habitat preference and threats in 2007. This survey has made a number of recommendations for further conservation work (Pierce et al. 2007). Conservation Actions Proposed
Carry out annual monitoring in May-June to determine whether the population is in decline and if so, where and what are the causes, and what contingency plan is best implemented (Pierce et al. 2007, Pierce 2010). Identify suitable habitat that supports the species. Advocate for protection of key habitats from fire, development etc, e.g. by engaging with key landowners, community and Government to identify risks, opportunities, solutions, etc and gaining better community buy-in (Pierce et al. 2007, Pierce 2010). Continue with rodent eradication from Kiritimati motu and monitor outcomes for seabirds and warbler (Pierce and Brown 2009). Use external advice to address biosecurity issues, e.g. spread of Pluchea and the potential arrival of invasive ants (Pierce et al. 2007). All surveyed sites should have the habitat described and rat trapping surveys completed. Implement rat trapping at important sites. Investigate the feasibility of emergency translocations to another island, e.g Orona in Phoenix Islands (Pierce et al. 2007).

Related state of the world's birds case studies

del Hoyo, J.; Elliott, A.; Christie, D. 2006. Handbook of the Birds of the World, vol. 11: Old World Flycatchers to Old World Warblers. Lynx Edicions, Barcelona, Spain.

Pierce R. 2010. Technical support and capacity building for the Wildlife Conservation Unit and Quarantine at Kiritimati, Kiribati, Report No. 2 December 2010. Eco Oceania Pty Ltd Report for Government of Kiribati and NZAID.

Pierce R., Brown, D. 2009. Technical support and capacity building for the Wildlife Conservation Unit and Quarantine at Kiritimati, Kiribati, May-June 2009. Eco Oceania Pty Ltd Report for Government of Kiribati and NZAID.

Pierce, R.; Anderson, R.; VanderWerf, E; Young, L. 2007. Surveys and capacity building in Kiritimati (Christmas Island, Kiribati), June 2007, to assist in restoration of populations of Bokikokiko and seabirds.

Pratt, H. D.; Bruner, P. L.; Berrett, D. G. 1987. A field guide to the birds of Hawaii and the tropical Pacific. Princeton University Press, Princeton.

Sherley, G. 2001. Bird conservation priorities and a draft avifauna conservation strategy for the Pacific Islands region. South Pacific Regional Environment Programme, Samoa.

Further web sources of information
Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Click here for more information about the Alliance for Zero Extinction (AZE)

Explore HBW Alive for further information on this species

View photos and videos and hear sounds of this species from the Internet Bird Collection

Text account compilers
Bird, J., Butchart, S., Derhé, M., Ekstrom, J.

Marks, T., Millett, J., Pierce, R., Wegmann, A.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2016) Species factsheet: Acrocephalus aequinoctialis. Downloaded from on 26/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 26/10/2016.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Kiritimati reed-warbler (Acrocephalus aequinoctialis) 0

Key facts
Current IUCN Red List category Endangered
Family Sylviidae (Old World warblers)
Species name author (Latham, 1790)
Population size 2500-9999 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 460 km2
Country endemic? Yes
Links to further information
- Additional Information on this species